Method of grinding and polishing gem facets



Oct. 28, 1947'. G. H. RAKOWITZKY 2,429,961

METHOD OF GHENDING AND POLISHING GEM FACETS Filed March 31, 1944 4 Sheets-(Sheet 1 IN VEN TOR.

G. H. RAKOWITZKY Oct. 28, 1947.

- METHOD OF GRINDING ANDPOLISHING GEM FACETS 4 Sheets-Sheet 2 Filed March 31, 1944 my? pimyfl G. H. RAKOWITZKY METHOD OF GRINDING AND POLISHING GEM FAGETS Filed Marqh s1,

' 1944 4 Sheets-Sheet 3 INVENTOR.

Oct. 28, 1947. e. H. RAKOWITZKY 2,429,961

1 METHOD OF GRINDING Ayn POLISHING GEM moms Filed March 31, 1944 4' Sheets-:Sheet 4 INVENTOR.

Patented Oct. 28, 1947 METHOD OF GRINDING AND POLISHING GEM FACETS Gregor'H. Rakowitzky, Brooklyn, N. Y., assignor of one-half to Joseph Alster, New York, N. Y.

Application March 31, 1944, Serial No. 528,884

1 Claim.

This invention relates to a method for grinding and polishing the facets of diamonds and other gems for use in the lapidary art and in the technical and industrial arts.

One object of the invention is to provide an improved grinding or polishing method whereby better results are obtained in less time without impairing the grinding surface.

Another object is the provision of a machine of improved construction and operation, and still another object is to provide gem holders or dops of such construction that the gems are handled with greater accuracy and security and without the aid of cements, adhesives, or similar anchoring agents.

With these and other objects in View my invention consists in the improved method and in the improved construction and arrangement of parts of the machine as hereinafter more fully described, by way of illustration or example and with reference to the accompanying drawings whereon:

Fig. 1 is a side view of a gem;

Fig. 2 is a diagrammatic plan view showing the grinding surface and the path of the gem;

Fig. 3 is a front view of the machine;

Fig. 4 is a detail view, partly in section, showing part of the driving gear for the grinder;

Fig. 5 is a detail view showing the opposite side of the gem carrier of Fig. 3;

Fig. 6 shows a part of said carrier as seen in the direction of the arrow 6, Fig. 3;

Fig. '7 is a part section and part side view of the gem holder or dop for use while grinding the base or pavilion facets;

Fig. 8 is a face view of the collar or index disc for use while grinding said facets.

In carrying out the improved method according to this invention, a grinding table 15, Fig. 2, is rotated at high speed about a vertical axis I8 while the gem is mounted ina holder carried at an angle corresponding to the angle of the facet to be ground and is caused to move continuously in a circular path l9 about a vertical axis so spaced from the axis of the table that the gem which contacts the grinding surface of the table is constantly changing its position with respect to the axis of the table and at the same time is constantly turning so that the grinding action of the table surface is applied to the gem at constantly changing angles with respect to the grain of the gem. As the table and-the gem are thus independently rotated-the former at a high and the latter at a relatively low angular speed--the portion of the table I5 engaged by 2 the gem forms an annular track defined by the concentric lines I5, I! which are of course concentric to the table axis l8, and the distance between the axis l8 and the line I6 is somewhat greater than the distance between the lines l6, 17, so that the relative speeds of the contacting surfaces of the table and gem do not materially change. In the preferred arrangement, the gem is moved in a clockwise direction in the path I9 while the table l5 also rotates clockwise so that the relative speeds of the par-ts at the points of contact are less variable. It has been found that satisfactory results are obtained with the table l5 making thirty or more revolutions to each revolution of the gem.

In operation the track between the lines [6, I1 is surfaced with oil and diamond dust or other abrasive in the known manner and this improved method has the characteristic feature that the grinding surface fails to show objectionable heatin while grinding diamond facets and turning at more than three thousand revolutions per minute. A further advantage of this method of moving the gem is that the grinding track between the lines it, I! remains smooth and serviceable indefinitely and the formation of circular grooves in the grinding surface is entirely avoided. In previously known machines for facet grinding the gem remained fixed (or rotated about a selfcontained axis) so that the grinding surface was soon grooved to such an extent that the grinding of flat facets became impossible.

Referring to Fig. 1 the dotted lines 20 indicate the outline of a gem that has been prepared by the formation of a table facet 2i and a culet 22 in readiness for the grinding of the facets.

The gem is then mounted in one of the holders or dops in the manner hereinafter described and the machine is operated to grind and polish the facets 24 below the girdle line 23 after which another holder or dop receives the gem and is adjusted to the proper angle for the grinding and polishing of the facets 25 above the said line 23. The gem at Fig. 1 is shown with eight crown or bezel facets 25 and an equal number of pavilion or base facets 24, but it will of course be readily understood that the invention also applies to the formation of gems in which the upper facets comprise star facets, bezel or top main facets, top corner facets, and top half or break facets, while the lower facets comprise bottom half or break facets, bottom corner facets, and pavilion or bottom main facets, or to the formation of other shapes, styles, or types of gems or stones wellknown in the lapidary art.

For the formation of the upper and lower facets the improved machine is preferably capable of adjustment for the grinding of facets of different angles, but the invention also contemplates the use of a series or battery of similar machines each adjusted to perform a different step or series or group of steps in the formation of the facets and also contemplates the formation of the various facets by two or more machines each incapable of adjustment for the grinding of more than a definitely limited group of facets, so that, for example, the facets 24 of Fig. 1 might be formed in one machine and the gem might then be transferred to another machine for the grinding of the facets 25.

The machine shown on the accompanying drawings is capable of adjustment and is provided with interchangeable parts whereby the various facets of the gem may be ground and polished Without undue heating of the gem and without grooving, scoring, or otherwise defacing the surface of the grinding member, and the operations may be performed by operators of minimum skill and experience.

Referring to Fig. 3 the machine is made with a base 26 having an opening for the passage of a sleeve 21 which extends downwardly from a collar 28 suitably secured to the base (see also Fig. 4), and mounted in suitable bearings in the sleeve 21 is spindle 29. The ends of the spindle extend beyond the sleeve 21 and the upper end has the rotary grinding table l of iron or other suitable material secured thereto while the lower end of the spindle has secured thereon a belt pulley 33 adapted to be driven by an electric motor (not shown) so that the table 55 is rotated at the desired speed. Also mounted on the base 26 is a bracket 3| having a foot portion 32 secured to the base 26 and having an integral horizontal part 33 projecting over the table I5 and formed at its extremity with a vertically disposed sleeve part 34 having suitable bearings for a spindle 35 adapted to rotate about a vertical axis so that the gem 36 is moved in the path [9 as above described with reference to Fig. 2.

The spindle 35 rotates with an enclosing sleeve 31 to which it is suitably keyed and secured to the upper part of the said sleeve 31 is a belt pulley 38 driven from an electric motor (not shown, but preferably mounted upon the bracket 31). The spindle 35 is free to move axially within the sleeve 3! and downward movement is limited by engagement of the pulley 38 by a nut 39 engaging the upper screw-threaded portion of the spindle. The nut 39 has a lock nut 40 also mounted upon the spindle 35 and the distance between the nut 39 and the pulley 33 is thus capable of fine adjustment so that such distance may determine the exact depth of the grind or cut of the gem 36. The said nut 39 is formed with a groove 4! in its outer periphery for engagement by a stud 42 projecting from a rocking arm 43 pivoted at 44 on a projection 45 on the bracket part 33. One end 46 of the arm 43 forms a handle while the opposite end 41 has its upper edge shaped to form recesses 48, 49 for engagement by a stud 53 on the upper end of a lever arm 5! pivoted at 52 on an extension 53 on the bracket, and the lower end of the arm 5| is extended to form a handle 54 by means of which the stud 5!] may be swung into position for engagement with the recess 49 after the handle 46 has been raised so as to lift the spindle 35 and the gem-carrying parts and thus stop the grinding or polishing operation. At the commencement of the operation the spindle 35 is set in motion and the handle 46 is first slightly raised and, while the handle 54 is swung to the right to disengage the stud 50 from the recess 49, the handle 46 is then moved slowly downwards to permit the weight of the gem-carrying parts to bring the gem into firm contact with the rotating surface of the table l5. The weight that gives the necessary grinding pressure is to some extent counterbalanced by the movable weight 55 adapted to slide along the arm 43 and having a set screw 55 by means of which it may be clamped in position for the desired pressure.

7 In order to provide a visual indication of the completion of each grinding operation the upper end of the spindle 35 is engaged by an adjustable set screw 5'! screw-threaded through a socket in one arm of a double-armed lever 58 pivoted upon a portion 53 of the said extension 45 and having a spring 63 holding the screw 51 in engagement with the end of the spindle 35. The second arm of the lever 53 is capable of engaging a short projection 61 integral with a relatively long pivoted arm 62 having an indicating button 63 on its upper end. These parts form the visual indicator and are carried in a casing 64 mounted on the said extension 45. The casing 34 is provided with a sight slot 55 and has a spring 66 by means of which the indicator button is normally held in the position shown. 7

When the grinding of the facet has been completed the nut 33 may rest upon the pulley 38 and the indicator button 63 is seen to vibrate in its slot 65. The operator then knows that the grinding has been completed, but he allows the machine to continue operating a little longer in order that the facet may receive a final polishing operation without pressure.

'Referring now to the gem carrier and to the holders or dops, the lower end of the spindle 35 (see Figs. 3, 5, and 6) has clamped thereon a cross-head 61 having ofiset from the spindle axis an opening for a pivot pin 68 integral with a cylindrical casing 69 which is clamped by means of the nut 70 at an angle appropriate to the angle of the facet to be ground, and a pointer H is mounted so as to swing with the casing 69 and to cooperate with a scale 12 to facilitate setting of the casing at the proper angle. The casing 69 serves as the carrier of the gem holders or dops which are adjustable andinterchangeable and are each provided with means for gripping and holding the gem. In Figs. 3, 5, and 6 the casing 69 is shown carrying the dop designed to grip and hold the gem during the grinding of the base or pavilion facets, and this dop and its parts are shown at Figs. 7 and 8.

Referring to Figs. 3, 5, 6, 7, and 8, the dop for holding the gem during the grinding of the base or pavilion facets 24 (Fig. 1) is mounted in a sleeve '13 carried in the casing 69 and having at its upper end a collar 14 provided with suitably spaced peripheral recesses 15 for engagement by a hinged retainer l6 mounted on a pivot pin 11 on the casing 69 so that the sleeve 13 may be locked by the retainer 16 in different angular posi tions corresponding to the different facets 24. The recesses 75 correspond in number to the number of facets in the base or pavilion of the gem and while Figs. 3, 5, and 6 show collars with eight recesses corresponding to the facets of the gem shown at Fig. 1, a collar with sixteen recesses is shown at Fig. 8, and interchangeable collars may be provided to conveniently adapt the machine to the handling of gems of various designs. The sleeve 13 may be provided at its lower end with nuts 78 to prevent axial movement and screws 19 or the like may also be provided for the purpose of tightening the casing 69 around the sleeve '13 to lock the latter against rotary movement when such locking is required. Fitted within the sleeve 13 is an inner tube 80 having its lower end (the left hand end Fig, 7) formed with an internal tapered or bevelled part 8| for engagement with a similarly tapered portion on a longitudinally split tubular part 82 whose slits 83 divide the projecting end into three segments forming jaws adapted to grip the gem as engagement with the tapered part 81 causes the said jaws to move inwardly. The said tubular part 82 is moved longitudinally for the closing of the jaws by the action of a sleeve member 84 having an actuating collar 85 and an externally screwthreaded portion for engagement with an internal screw-thread in the tube 89, and the latter is also screw-threaded externally for the reception of a washer 85 and nuts 81, and a latch device 88 on the collar 74 may be turned over the washer 86 to prevent relative movement of the parts in an axial direction. Centrally located in the dop is a stem 89 having screw thread engagement with the interior of the sleeve 84 and having an operating knob 98 and adjusting and locking nuts 9|. The inner extremity of the stem 89 is socketed for the reception of one end of an interchangeable stem part 92 whose opposite end is formed with a flat face I97 accurately formed at right angles to the axis of the dop and adapted to press firmly against the table facet 2| (Fig. 1) of the gem so that the latter is maintained in proper position to ensure accurate angular disposition of facets being ground. During the grinding operation the dop is prevented from rotating about its own axis by the engagement of the hinged retainer 16 with one of the recesses 75 in the collar 14, while suitable splines or keys (not shown) prevent rotation of the tube 80 within the sleeve 13.

In the operation of the machine the gem is held at the desired angles to the grinding surface and is caused to turn in a circular path spaced a substantial distance from the center of rotation of the grinding table, and for the adjustment of the angle of the dop with respect to the grinding surface the dop may be so arranged that its longitudinal axis lies in a plane that is substantially tangential to the said circular path so that changes in such angle do not to any material extent increase or decrease the diameter of said path and the effective grinding surface or track upon the table thus remains substantially the same, and, since grooving and scoring are entirely avoided, the surface in question remains in practically permanent condition for satisfactory operation. In practice it has been found that, due to the constantly varying line of contact between the work and the grinding surface, the results are unusually satisfactory and the grinding surface is improved rather than deteriorated by long use.

Although the drawings and the above specification dis-close the best mode in which I have contemplated embodying my invention, I desire to be in no way limited to the constructional details and arrangement of parts disclosed, for in the further practical application of my invention many changes may be made in the construction, arrangement, and dimensions thereof as circumstances require or experience suggests without departing from the spirit of the invention within the scope of the appended claim.

What I claim is:

A method of grinding and polishing gem facets which comprises rotating a flat annular lapping track about an axis at right angles thereto, holding the gem at an acute angle to said track during the lapping operation, preventing rotation of the gem about its own axis and rotating the gem in contact with said track and in a circular path about a fixed axis parallel to said first axis, the diameter of said circular path being substantially equal to the width of the annular lapping track, said circular path being to one side of the first axis. whereby the lapping action is applied to the gem at constantly varying angles with respect to the grain of the gem and whereby such grain is presented to the lapping track in parallel relation to the direction of movement of the contacting portion of such track twice during each rotation of the gem in its circular path.

GREGOR H. RAKOVVIT'ZKY.

REFERENCES CITED The following references are of record in the file of this patent:

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